1. Field of the Invention
The invention relates in general to a method of packaging flip chip and method of forming pre-solders on substrate thereof, and more particularly to a method of packaging flip chip and a method of forming pre-solders on substrate thereof use a patterned photo-resist film in printing a metal material.
2. Description of the Related Art
The conventional method of forming pre-solders on a substrate includes the following steps. The upper-surface solder mask of the substrate covers parts of the upper-surface metal circuits and parts of the upper surface for exposing several upper-surface pads.
Firstly, a stencil such as a screen or a steel plate covers the upper-surface solder mask. Several openings on the stencil correspond to the upper-surface pads. Then, several metal materials are printed in the openings. Afterwards, a force is applied to separate the stencil from the substrate. After the stencil is removed, the metal materials are left on the upper-surface pads. Finally, the metal materials are reflown to form several pre-solders.
However, in the step of separating the stencil from the substrate, the metal materials are easily carried away by the openings of the stencil. FIG. 1 is a diagram showing the removal of a stencil when the pre-solders of a conventional substrate are formed. When the stencil 132 is separated from the substrate 100, due to the external force, the openings 134 of the stencil 132 are easy to be stained by parts of the metal material 136a or carry the metal material 136b away, resulting in the shortage of solders and affecting the subsequent process. Particularly, the scale of the substrate is designed to be smaller and smaller, thereby having fewer amount of solder on each pad. That the stencil carries parts of the metal material away severely affects the amount of solder. Besides, the scale of the substrate is designed to be smaller and smaller, and the pitches of the substrate are designed to be narrower accordingly, so the substrate requires a higher standard of precision. Therefore, the conventional method of using a screen or a steel plate as the stencil in the method of forming pre-solders on substrate can not meet the precision requirement of the substrate.